The present invention relates, according to the preamble of claim 1, to a device for loading and unloading of optical workpieces, in particular optical lenses, for a lens machine with a loading arms driven swivellable about an axis which in controlled movement processes swivels between a workpiece magazine and the processing station on the lens machine and at its outer end is fitted with a device for picking up and depositing workpieces. Although the description below discusses only the loading or unloading of workpieces, the device is however equally suitable for tool changing.
Automatic loading systems for lens machines are becoming increasingly important because of rising personnel costs. Such loading systems have to take into account a wide range of workpieces, high accuracy requirements and small batch sizes. According to the state of the art there are three different construction concepts, namely (1) devices with cam-controlled loading arms, (2) devices with pneumatic loading arms driven by cylinders and swivel rotors and (3) devices which for loading or unloading use the CNC axes present on the lens machines.
(1) Cam-controlled loading arms have been in use for decades (e.g. DE-PS 12 38 802). Such cam-controlled loading systems require great expense in set up and adjustment, offer no facility for influencing the speed of the movementxe2x80x94which is very important with different workpiece weightsxe2x80x94and can only approach established, unchanging loading and unloading positions.
(2) Pneumatic loading arms driven by cylinders and swivel rotors with automatic stops and dampers are used today in various lens machines. Known automation systems for lens machines (e.g. EP 0 090 752 A1, EP 0 175 431 B1, U.S. Pat. No. 2,933,863) work using pneumatic drive elements with complex devices requiring costly maintenance. Because of the compressibility of compressed air and the stick-slip effect occurring on the pneumatic cylinders, these systems have disadvantages. In these systems the force with which the loading system is set in movement can be restricted relatively simply by restricting the pressure of compressed air, but difficulties occur with an external movement restriction of the loading arm. When this restriction is not present, namely very rapid swivel or linear movements result which lead either to the workpieces being flung off or at least displaced and hence to a change in workpiece position. Furthermore in pneumatically operated loading systems the stops shift due to wear and/or vibration. The movement speed is affected by external influences e.g. the lubrication state of the mechanics and the compressed air, the soiling of the mechanical elements involved or the amount of pressure in the compressed air. This is particularly critical when loading large delicate workpieces. To summarise it can be found that the precision and reliability of the workpiece insertion using such loading systems are relatively low. In addition, such systems can also approach only a few established positions of the loading arm.
(3) Recently more attempts have been made to achieve the supply to lens machines using the existing CNC axes of the lens machine (e.g. DE 198 25 922 A1). The carriages of the horizontal movement axes are moved over long distances, where a piston-cylinder arrangement mounted on one of the carriages collects the workpieces with a suction device from a magazine arranged outside the processing area of the lens machine. This design is indeed flexible and works relatively precisely in position, but large masses must be moved over long distances, leading to relatively long change times. Also the CNC axis can only be used for the feed process when the actual machining processes on the lens machine have previously been completed. A prepositioning of the optical lens to be machined close to the chuck of the workpiece spindle during machining of another lens is not possible. In addition the longer linear axes necessary cause a considerable increase in production costs of such lens machines and also lead to larger and hence heavier machines.
Finally, as the state of the art which does not concern lens machines directly, reference is made to the publications DE 40 37 773 A1 and DE 198 30 365 C1.
DE 198 30 365 C1 discloses a rotary stroke drive with a stroke drive unit coupled to a rotary drive unit. Here the stroke drive unit has a gear motor arranged in a stroke drive housing for stroke drive of a threaded spindle, and the rotary drive unit has a gear motor arranged in a rotary drive housing for rotary drive of an output shaft, which are arranged coaxial to each other and connected together via a coupling unit to transfer the stroke to the output shaft. The output shaft itself can be connected with a robot arm which carries a sucker for collection and deposit of e.g. workpieces.
DE 40 37 773 A1 discloses a swivel arm robot with a rotary stroke unit which has a spindle sleeve and arranged thereon a gripper holder which is rotatable about a rotary axis and longitudinally mobile in the vertical direction. The construction elements which achieve the translatory and rotatory movement of the spindle sleeve are not described in detail in this state of the art.
The present invention is therefore based on the task of producing a device for loading and unloading of optical workpieces, in particular optical lenses, which avoids the said disadvantages of the former systems and allows a compact and simple structure with a high loading and unloading precision.
According to the invention in a device for loading and unloading optical workpieces for a lens machine with a loading arm driven swivellable about an axis, which arm can swivel in controlled movement processes between a workpiece magazine and the machining station on the lens machine and at its outer end has a device for picking up and depositing workpieces, the swivel axis of the loading arm is the centre axis of a spindle rotating in both directions of rotation and drivable mobile in linear strokes in both axial directions by drive elements and guided rotatably and displaceably in guide elements, on which spindle is attached the loading arm, where the spindle is designed both as a splined shaft and as a threaded spindle and is guided by two rotatably mounted, fixed location nut elements forming the guide elements, of which one nut element engages with the splined shaft and the other nut element with the threaded spindle, where the nut elements can be driven individually or simultaneously, in opposite or the same direction of rotation.
Thus an essential feature of the invention is the use of a special spindle equipped with several overlaying degrees of movement freedom, the movement processes of which can be freely programmed, preferably independently of the control of the machining processes being performed on the lens machine. This spindle guides and controls in a compact, simple and stable manner all movements of the loading arm i.e. both its stroke and its rotation movements, without end-of-travel stops being required. In this way the loading arm can approach any intermediate positions at which the device can be fitted with equipment for additional work processes such as precentring, turning or rotating, measuring or washing of the lens. As the loading arm in each direction can be guided over any long or short swivel or stroke movements, all movement processes can be performed with optimum travel and hence time. A spindle which can be used for the purposes of the invention is available commercially under the name xe2x80x9cBall Screw Splinexe2x80x9d type BNS from the company THK Co. Limited, Tokyo, Japan. Finally in this connection it should also be stated that the device provided on the loading arm for picking up and depositing workpieces can for example be a vacuum-operated suction element adjustable in height to pick up lenses of different thicknesses against spring force, or a gripper or clamping element driven by compressed air.
In an advantageous embodiment of the invention, the spindle with the loading arm, its drive elements and guide elements is attached to a frame which as a self-contained system carrier can dock on the lens machine in a defined position to the workpiece spindle of the lens machine so that the workpiece spindle of the lens machine lies on a swivel circle of the loading arm device. Thus the device can be used as a loading system on any lens machine e.g. fine grinding, polishing, centring or lens edge machining apparatus, even by subsequent fitting. The frame of the invention is there preferably docked on the front side of the lens machine concerned and as a self-contained system carrier can carry or contain all mechanical elements such as also the electronic controls, the operating and display elements (keyboard/screen) and the pneumatics for the device provided on the loading arm for picking up and depositing workpieces. The frame of the device can in a compact construction also have a cylindrical metal sleeve which holds the nut elements according to the invention and protects these against soiling.
In a further development of the inventive concept, the frame can dock on the lens machine at its lower end via swivel pins and at its upper end via screws and stops which can be adjusted to achieve in a simple manner the axial parallelity between the spindle and the workpiece spindle of the lens machine. As a result after release of the screws the device can be swivelled away to the front whereby e.g. the workpiece spindle of the lens machine is easily accessible for maintenance or repair purposes without hindrance from the device. Alternatively or in addition the frame can also be attached swivelling to the side on the lens machine. Here also adjustable stops and screws can be provided which serve to set the rotary axis distance from the spindle and workpiece spindle.
In a suitable embodiment of the device the first of the two nut elements is attached to the frame at the top by means of the associated support bearing whereas the second nut element is attached to the frame at the bottom by means of the associated support bearing axially aligned with the first nut element, where to each nut element is allocated a drive motor attached to the frame, preferably a stepper motor, which via a toothed belt is in drive connection with a pulley coaxially attached to the associated nut element.
In the further development of the invention at the lower end of the totally hollow spindle can be applied a rotary passage through which a vacuum can be applied and/or compressed air supplied to the device of the loading arm. By using the spindle itself as a supply or guide element, the pneumatic pressure can easily be applied to the loading arm device.
In an advantageous refinement of the invention, on the frame of the device are preferably fitted two magazines for blanks and finished workpieces, the collection and deposit positions of which are on the swivel circle of the loading arm device. The workpieces to be processed or already processed are stored in these magazines so that they can be guided into the relevant collection position or from the deposit position. Preferably the two magazines are rotatable or where applicable exchangeable plate magazines which are symmetrically arranged at the side andxe2x80x94viewed from the frontxe2x80x94in front of the spindle, and the rotary axes of which are aligned parallel to the spindle and allocated to each of which is a freely programmable and indexable drive attached to the frame. Thus advantageously there is a good adaptation facility to different workpiece sizes and geometries. As an alternative to the magazine, according to the relevant requirements, a conveyor belt for recipe or lens transport cases can be arranged in relation to the swivel circle of the loading arm device such that by means of the loading arm device, blanks and finished workpieces can be collected from or deposited in correspondingly positioned boxes by means of the conveyor belt.
According to the requirements also between the two above-mentioned magazines on the frame can be arranged a centring station for the workpieces with its centre on the swivel circle of the loading arm device. Using such known centring stations, workpieces with tolerances can be precentred after collection from the blank magazine in order to allow precise insertion of the workpiece in the chuck of the workpiece spindle.
The device can also have a workpiece turning device fitted to the frame on the swivel circle of the loading arm device. With this it is possible to use the device also to feed a lens machine for bilateral surface machining on the workpiece.
Finally in a further refinement of the inventive concept, the loading arm can be formed as a V-shaped double arm with at each arm end devices to pick up and deposit workpieces, which devices lie in the same swivel circle and can be connected independently with a vacuum and/or compressed air source. This measure achieves a particularly rapid workpiece change for example by the device on one arm end transporting a blank workpiece and the device on the other arm end transporting a finished workpiece. In this case through the preferably hollow spindle are guided two separate pneumatic lines in order to supply energy to the two devices at the arm ends at different times. To this end in the spindle can be inserted a tube, where applicable concentric to the spindle, where the interior of the tube and the annular space between the outer peripheral surface of the tube and the inner wall of the spindle can be supplied with vacuum and/or compressed air separately from each other via the rotary passage.